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1.
太阳活动低年夏季,低纬电离层F区场向不规则体表现出与太阳活动高年和其他季节明显不同的特征.本文利用我国三亚站（18.4°N,109.6°E,地磁倾角纬度dip latitude 12.8°N）VHF雷达、电离层测高仪、GPS闪烁监测仪和美国C/NOFS卫星观测数据,研究了太阳活动低年夏季我国低纬电离层F区场向不规则体的基本特征.分析发现无论磁静日还是磁扰日,夏季电离层F区不规则体回波主要出现于地方时午夜以后,回波出现的时间较短,高度范围较小,伴随着扩展F出现,但没有同时段的L波段电离层闪烁.太阳活动低年夏季午夜后的低纬电离层F区不规则体回波,可能并不总是与赤道等离子体泡沿磁力线向低纬地区的延伸相关,而可能由本地Es等扰动过程引起. 相似文献
2.
本文阐述了利用GPS接收机台阵测量到的闪烁和TEC变化率ROT快速起伏图样估计F层不规则结构漂移的原理和方法,并利用实测数据估计了静日和暴时电离层不规则结构的水平漂移速度.短间距台网和超短间距台链观测实例的计算结果表明,暴时武汉地区引起TEC快速起伏的电离层不规则结构沿纬圈向西漂移,21∶30至03∶00 LT,西向漂移速度在约40 m/s至130 m/s的范围内变化;在桂林地区,磁静日午夜前后引起L波段电波闪烁的电离层不规则结构沿纬圈向东漂移,漂移速度从约70 m/s下降到约55 m/s,磁扰日午夜前不规则结构向西漂移,速度从约150 m/s下降到约50 m/s,午夜后转为向东漂移,速度从约25 m/s上升到约65 m/s.文中还提出了由单站多卫星观测估计F层不规则结构漂移的设想.实例分析与计算结果表明,利用单站多卫星观测估计电离层不规则结构漂移是一种合理可行的方法. 相似文献
3.
《Journal of Atmospheric and Solar》1999,61(16):1219-1226
With increasing reliance on space-based platforms for global navigation and communication, concerns about the impact of ionospheric scintillation on these systems have become a high priority. Recently, the Air Force Research Laboratory (AFRL) performed amplitude scintillation measurements of L1 (1.575 MHz) signals from GPS satellites at Ascension Island (14.45° W, 7.95° S; magnetic latitude 16° S) during February–April, 1998, to compare amplitude scintillations with fluctuations of the total electron content (TEC). Ascension Island is located in the South Atlantic under the southern crest of the equatorial anomaly of F2 ionization where scintillations will be much enhanced during the upcoming solar maximum period. Ascension Island is included in the global network of the International GPS Service (IGS) and the GPS receivers in this network report the carrier to noise (C/N) ratio, the dual frequency carrier phase and pseudorange data at 30-s intervals. Such data with a sampling interval of 30 s were analyzed to determine TEC, the rate of change of TEC (ROT) and also ROTI, defined as the standard deviation of ROT. The spatial scale of ROTI, sampled at 30 s interval, will correspond to 6 km when the vector sum of the ionospheric projection of the satellite velocity and the irregularity drift orthogonal to the propagation path is of the order of 100 m/s. On the other hand, the scale-length of the amplitude scintillation index corresponds to the Fresnel dimension which is about 400 m for the GPS L1 frequency and an ionospheric height of 400 km. It is shown that, in view of the co-existence of large and small scale irregularities in equatorial irregularity structures, during the early evening hours, and small magnitude of irregularity drifts, ROTI measurements can be used to predict the presence of scintillation causing irregularities. The quantitative relationship between ROTI and S4, however, varies considerably due to variations of the ionospheric projection of the satellite velocity and the ionospheric irregularity drift. During the post-midnight period, due to the decay of small scale irregularities leading to a steepening of irregularity power spectrum, ROTI, on occasions, may not be associated with detectable levels of scintillation. In view of the power law type of irregularity power spectrum, ROTI will, in general, be larger than S4 and the ratio, ROTI/S4, in the present dataset is found to vary between 2 and 10. At high latitudes, where the ionospheric motion, driven by large electric fields of magnetospheric origin, is much enhanced during magnetically active periods, ROTI/S4 may be considerably larger than that in the equatorial region. 相似文献
4.
The scattered reflections and multiple traces regularly recorded on the topside sounding ionograms of the Interkosmos-19 satellite in the frequency range of 7–10 MHz are considered. The reflected radio signals in this frequency range appear both above and below the critical frequency of the regular layer F2. They are observed at all altitudes of the topside ionosphere from hmF2 to a satellite altitude of 1000 km. It is shown that these phenomena regularly appear at high latitudes (≥60° ILAT) and, less often, in the equatorial region. The scattered reflections indicate the presence of small-scale irregularities, and continuous traces are a consequence of total internal reflection from large-scale irregularities. Small-scale irregularities evidently form within a large-scale irregularity. Ray tracing shows that the size of large-scale irregularities is hundreds of kilometers in height and tens of kilometers in latitude. The appearance of scattered reflections and multiple traces at high latitudes is nearly independent of local time; in the equatorial region, they appear only in the interval of 20–08 LT. All of this agrees well with other observations of irregularities in the ionospheric plasma of different scales. 相似文献
5.
中低纬电离层E区不规则体准周期雷达回波现象,在地球不同经度区被观测到并开展了有关研究.本文利用三亚(109.6°E,18.4°N)VHF相干散射雷达2011年2月6日的观测,第一次给出了中国低纬电离层E区准周期回波的发生和变化特征.观测结果表明:准周期回波发生在地方时夜间2100—2200LT的110km高度上,与连续性回波可同时发生;准周期回波斜纹在雷达探测的高度-时间-强度(HTI)图上可延伸5～20km,持续时间为5～15min,回波斜纹高度随时间以20～30m/s下降,斜纹在HTI图上彼此间隔10km和10min左右.此外,雷达回波多普勒谱和雷达干涉分析显示不同高度准周期回波的多普勒速度随高度-时间表现出不同的变化趋势,与回波条纹斜率无明显联系,不同高度准周期回波对应的不规则体在东西方向也表现出截然不同的运动特征.分析结果表明,三亚电离层E区准周期回波的发生可能并不是由散块Es随着中性风周期性的经过雷达探测区域所致,而可能和Es中的扰动结构相关. 相似文献
6.
本文基于IRI模型、地面数字测高仪和GNSS TEC数据,提出了一种利用经验正交函数(Empirical Orthogonal Function,简称EOF)估算顶部电离层电子密度剖面的方法,并将其应用于美国Millstone Hill测高仪和GNSS数据以估算顶部电离层电子密度剖面.通过将估算的临界频率、峰值高度、400km以上电子密度分别与测高仪实测临界频率、测高仪实测峰值高度以及非相干散射雷达实测400km以上电子密度作对比以对方法的有效性进行验证.统计结果显示估算临界频率、峰值高度与测高仪实测数据基本一致,400km以上估算电子密度相较于非相干散射雷达实测的绝对误差平均值仅是测高仪推算400km以上电子密度绝对误差平均值的一半左右.所以本文提出的方法可以更加精确地估算顶部电离层电子密度. 相似文献
7.
根据电离层不规则体的产生会导致周围电子浓度发生起伏变化的原理,利用2007年COSMIC掩星系统的TEC数据,通过平滑滤波得到TEC的扰动值ΔTEC的变化,利用其研究F层不规则体的时空变化特征.统计结果表明:扰动较大的掩星事件主要发生在磁纬±20°之间和高纬地区,春季和秋季带状分布较为明显,不同经度地区较强扰动的掩星事件的分布也有不同特征;较强ΔTEC的掩星事件主要发生在地方时午夜前和午夜后两个时段,发生的高度主要在250~400km范围内.这些结果与已知的F层不规则体的时空分布特征较为一致,说明利用TEC的扰动量来分析电离层F层不规则体结构是可行的. 相似文献
8.
E.R. de Paula E. Alam Kherani R.Y.C. Cueva L.A.P. Camargo 《Journal of Atmospheric and Solar》2011,73(11-12):1544-1554
The statistics of pre-midnight 5-m irregularities in the equatorial F region over São Luís is presented. The data set ranges from October 2001 to December 2008 and covers maximum solar-flux-to-minimum solar flux epoch. The variabilities in irregularity parameters, namely, height and time of their appearance in the radar echoes, with solar-flux variation are presented. The seasonal variations (combined over all years, irrespective of solar-flux) of occurrence of irregularities, occurrence of bottom-type layer (or bottom-side irregularities without plume) and bottom-side/topside plume (or bottom-side irregularities with plume) are presented. The largest occurrences of bottom-side irregularities without plume and with plume are found on April (equinox) and December (summer) months respectively. The ambient ionospheric conditions namely prereversal evening vertical drift, bottom-side density gradient and off-equatorial E region conductivity are inferred using digisonde measurements during April 2002 and December 2002. Based on these conditions and recent studies on gravity wave climatology over Brazil, it is suggested that shear in zonal plasma drift and low gravity wave activity may account for less occurrence of plume during April as compared to December months. This suggestion is quantified using numerical simulation model of collisional-interchange instability (CII) and plasma bubble. 相似文献
9.
V. L. Khalipov A. E. Stepanov G. A. Kotova S. E. Kobyakova V. V. Bogdanov A. B. Kaisin V. A. Panchenko 《Geomagnetism and Aeronomy》2016,56(5):535-544
Vertical and horizontal plasma drifts are investigated during the polarization jet (PJ) detection in the F2 ionospheric layer based on the Doppler measurements at the Yakutsk meridian chain of subauroral ionospheric stations. It is shown that the velocities of vertical and horizontal drifts are significantly higher than the background motion during PJ observation periods. The ionospheric plasma motion direction changes from upward to downward on the polar edge of the main ionospheric trough. Doppler measurements on the DPS-4 ionosondes are compared with the simultaneous measurements of the plasma drift on the DMSP satellites during their passage near the Yakutsk meridian. The two kinds of measurements are in good agreement with each other. During the magnetic storm of June 23, 2005, by measurements of the DMSP satellites, the velocities of upward plasma flows were 1.0–1.4 km/s at a satellite altitude of 850 km. In the ionospheric F region, this speed corresponds to 150 m/s. According to satellite measurements, the westward drift velocity reached 2.5 km/s. The development of the polarization jet in the ionosphere was accompanied by a tenfold decrease in the electron density in 15–30 min. 相似文献
10.
Nathan Blaunstein 《Annales Geophysicae》1995,13(6):617-626
In contrast to the way that the spreading of irregularities in a plasma is usually considered, the diffusion spreading of irregularities stretched along the geomagnetic field B is examined using a three-dimensional rigorous numerical model of quasi-neutral diffusion in the presence of a magnetic field, in conjunction with the actual height variations of the diffusion and conductivity tensors in the ionosphere. A comparison with the earlier constructed approximate model of unipolar diffusion was made. As in the previous case, the same peculiarities of irregularity spreading in the inhomogeneous background ionospheric plasma were observed. The accuracy of the approximate model for describing the process of spreading of anisotropic ionospheric irregularities is established. Time relaxation effects of real heating-induced ionospheric irregularities on their scale transverse to B are presented using the approximate analytical model for the case of a quasi-homogeneous ionospheric plasma. The calculated results have a vivid physical meaning and can be directly compared with experimental data on the radiophysical observations of artificial heating-induced irregularities created by powerful radio waves in the ionosphere. 相似文献
11.
基于三亚(109.6°E,18.4°N)VHF电离层相干散射雷达观测,分析了我国低纬电离层E区场向不规则结构连续性回波的发生特征.研究结果表明:白天,E区连续性回波的多普勒速度范围为-50至25m/s,多普勒宽度主要分布在20至70m/s;连续性回波的高度大约以1km/h的速度缓慢下降,与偶发E层(Es)底部所在高度(hbEs)有很好的相关性,表明在背景电场影响下,Es经梯度漂移不稳定性产生场向不规则结构,引起E区连续性回波.夜间,E区连续性回波的多普勒速度范围为-50至50m/s,多普勒宽度为20至110m/s,回波在时间-高度-强度图上常呈现多层结构,可能与潮汐引起的多个离子层相关;而E区连续性回波的短暂中断,以及120km以上高E区连续性回波的发生,则可能归因于赤道扩展F极化电场的影响.此外,对E区连续性回波多普勒速度与全天空流星雷达风场观测的比较发现,在100km以下,多普勒速度与子午风场有很好的相关性. 相似文献
12.
在地面上用无线电方法研究电离层时,通常只利用电离层反射的一次回波,但是利用二次回波来研究电离层也是可能的。利用二次回波提供的补充知识,特別是利用一次和二次回波的同时观测结果的相互对比,在某些情况下,对电离层物理和电波传播的研究,具有特别的意义。在这篇文章中,将对垂直採测时从电离层反射的二次回波波場和振幅的统计特性,以及一次和二次回波之间的统计联系,进行一些理论上的计算;并根据这些计算结果,讨论一下利用二次回波研究电离层和电波传播吋的若干问題。 相似文献
13.
在地理坐标系下推导出二维电离层发电机理论方程,采用逐线迭代法求解得到全球二维电离层发电机电流函数,进而得到电离层发电机电流和电场.模式中使用的电导率是根据外部经验模式给出的背景大气和电离层参数,采用理论公式计算得出;输入的中性风场和磁场分别由HWM93和IGRF2000模型给出,该电离层发电机理论模式很好地给出了全球Sq电流形态及电离层E层发电机电场的基本特征.利用该模式研究了外部模式风场以及地磁场随高度的变化对模拟结果的影响,发现在90~180 km高度上,风场随高度变化对电流影响较大,而地磁场影响较小;重点模拟研究了地磁平静时期,Sq电流涡旋中心位置和总电流强度的变化规律,初步研究发现,电流中心位置在地理纬度±30°附近,不同的地方时电流随地磁纬度线平行移动,且南北半球两个电流涡中心电流强度之和变化不大.分析发现这种规律与发电机高度上的磁场总强度及地磁倾角的全球分布有很好的相关性. 相似文献
14.
A large sample of summertime data from the McGill Radar Weather Observatory was analyzed to determine the variation with altitude
of the horizontal extent of individual rainshowers. For echoes defined by a reflectivity factor of 39 dBz (equivalent to a
rainfall rate of about 10 mm/h) it was found that the mean area of the total population of echoes decreases linearly with
altitude from approximately 20 km2 at 2 km to 11 km2 at 8 km. Subsets of the total population were investigated, consisting of only the echoes penetrating the altitudes of 6,
7, and 8 km. On the average these relatively tall echoes are much greater in horizontal extent than the total population.
Whereas the sizes of the total population of echoes at any altitude are distributed approximately exponentially in terms of
the square root of area, the sizes of the “survivors” that extend to high altitudes may be described by the gamma distribution
with a mean value decreasing approximately linearly with height above 3 km and a dispersion of 0.55. Some characteristics
are also reported for echoes defined by reflectivities of 31 dBz and 47 dBz. Estimates are given of the fraction of the total
area in a horizontal plane that contains echoes in each of these categories. 相似文献
15.
The parameters of the neutral atmosphere have been studied using artificial periodic irregularities of the ionospheric plasma. A few measurement cycles were carried out in 2006–2007 using the new method, in particular: irregularities were created by powerful radiowaves at two separated frequencies. The possibilities of the method have been demonstrated. Based on the relaxation times of artificial periodic irregularities measured at two frequencies, the N(z) electron density profiles in the 95–115 km height interval have been determined and have been used to estimate the parameters of the neutral atmosphere. The results of determining the temperature and density of the neutral atmosphere are presented and compared with the data obtained earlier. 相似文献
16.
T. D. Borisova N. F. Blagoveshchenskaya V. A. Kornienko M. T. Rietveld 《Geomagnetism and Aeronomy》2007,47(1):76-84
The method for estimating the behavior of the ionospheric irregularity motion vector in the artificially disturbed HF ionospheric region has been proposed, and this behavior has been analyzed based on the simultaneous Doppler observations performed on several paths using the method of bi-static backscatter of diagnostic HF signals by small-scale artificial ionospheric irregularities. The Doppler measurements were performed during the modification of the auroral ionosphere by powerful HF radiowaves emitted by the EISCAT heating facility (Tromsø, Norway). It has been obtained that the dynamics of the ionospheric irregularity directions in the F region, calculated based on the Doppler measurements of the total vector of the ionospheric irregularity velocity above the Tromsø EISCAT radar at a frequency of 931 MHz, is in satisfactory agreement with such calculations performed using the three-position method. 相似文献
17.
18.
The problem of radiosignal reflection from a plane layered isotropic ionosphere has been considered. The vertical sounding ionograms for ionospheric layers with a complicated structure have been modeled. It has been demonstrated that the structure of reflected signals depends on the degree of ionospheric irregularities. Diffuse reflection of radiosignals, caused by the vertical irregularity of the ionosphere, has been detected. 相似文献
19.
A large sample of radar data from the period May–August 1976 was analyzed to provide information on the total areal coverage of precipitation echoes at 1-km steps in altitude ranging from 2 km up to 10 km. A transformation based on known statistics of surface rainfall rate was employed to express this information in terms of the probability of certain reflectivities being exceeded at a randomly chosen point at a given altitude. The same data base was used to construct a family of average vertical profiles of precipitation reflectivity. The profiles were conditioned by the reflectivity value at the lowest level (2 km), thus providing a basis for estimating the reflectivity aloft, given the low level or surface rainfall rate. Analyses of this kind have been reported for other geographical locations and for a variety of applications, such as hydrology, rain effects on earth-space radio propagation, and precipitation modeling. Similarities in the results from these two quite different analysis procedures, possibly not hitherto recognized, were found in the present study. 相似文献
20.
A. Bourdillon E. Lefur C. Haldoupis Y. Le Roux J. Menard J. Delloue 《Annales Geophysicae》1997,15(7):925-934
HF radar observations of mid-latitude sporadic-E irregularities carried out with the Valensole radar in South France are compared with simultaneous ionosonde measurements underneath the irregularity zones. In a previous study of Valensole radar data, it has been shown that HF backscatter from the night-time mid-latitude E region is usually associated with largescale wave-like modulations. To obtain more information on the geophysical conditions prevailing during backscatter events, a new experiment was performed which also included a vertical ionosonde beneath the scattering region. The data to be presented here are from two periods when radar scattering appeared simultaneously with large variations in the virtual height and the Doppler velocity of F-layer reflected echoes measured with the vertical ionosonde, indicating very clearly the passage of atmospheric gravity waves (AGWs). The effect of the atmospheric waves on the sporadic-E layer is not always as marked as it is in the F region. In the first event, the passage of the AGWs is accompanied by an upward followed by a downward movement of the Es-layer. The apparent descending movement of the Es-layer from 135 to 110km in less than 10 min corresponded to a positive (downward) Doppler velocity of 35 m/s measured by the vertical ionosonde, and was accompanied by a range variation in the radar scattering region with a negative rate of about 90–110 m/s. In the second event, the Es-layer is not as strongly disturbed as in the previous one, but, nevertheless, the range variations of the scattering region can still be associated with height fluctuations of the Es-layer. 相似文献